Acids are used to catalyze reactions in a number of different syntheses in the refining, chemical, petrochemical, and pharmaceutical industries among others. Acids may also be formed from syntheses, as reaction byproducts. When the stream is a gas, it is often desired to eliminate the acid from the gas. Elimination of the acid from the gas is traditionally accomplished by means of base neutralization that typically involves a caustic scrubbing process. That is, a base in the form of a liquid is added to the gas to neutralize the acids.
Typically, an excess of the base neutralizer must be added to assure complete removal of acid. The neutralization of the acid by the base neutralizer results in salt byproducts being formed. Following the acid neutralization process, the excess base neutralizer and salt byproducts must be removed.
Since the base is a liquid and a separate phase from the fluid, the neutralization is generally accomplished in columns where the base is dispersed into the gas to facilitate the neutralization. The gas bubbles rise up the column, contacting the liquid base. The excess base and reaction byproducts are subsequently removed at the bottom of the column. The efficacy of this system is related to the mass transfer efficiency between the two phases. This is directly related to the specific contact area (area per unit volume) that is available for mass transfer. To increase this area, many columns will typically use either structured or unstructured packing. The limited specific contact area possible necessitates increasing the size of the packing. The gas stream, exiting the column will typically entrain with it, an aerosol of base neutralizer that may cause challenges downstream. Therefore, it is necessary to introduce a high-efficiency aerosol-removal separator downstream. Typically, then, the mass transfer between the liquid and gas, and the complete separation of the liquid from the gas occur in two separate devices.
A disadvantage of the above conventional two-stage acid neutralization process is associated with the capital costs for the hardware such as towers and reaction tanks.
Similarly, in the refining and other industries, gaseous hydrocarbon streams that contain a range of hydrocarbons are stripped of the heavier hydrocarbon components through absorption into absorption oil in an absorber column or an absorber stripped column.
The present invention provides a process for the removal of an unwanted component from a gas by introducing an extracting liquid to extract the unwanted component from the gas through an interaction between the extracting liquid and the unwanted component. In a preferred embodiment, the volume of extracting liquid can be generally the same as the volume of the component to be extracted. More specifically, this invention relates to the process of creating an aerosol of an extractive liquid, capturing this aerosol on a high specific area microstructure to effect the extraction of the unwanted component and separation of the liquid phase within this microstructure. The extraction occurs from the gas to a liquid phase that is either stably dispersed in the primary phase gas or a film on the porous medium. In the case of the removal of an acid from a gas, the process involves creating an aerosol or dispersion of a polar liquid phase that is stably dispersed in the gas stream and forms a film on the porous medium. In the case of removing heavier hydrocarbons, the process involves creating an aerosol or dispersion of an extractive liquid that oleophilically interacts with the heavy hydrocarbons in the gas to form a “rich” oil phase that is stably dispersed in the light hydrocarbon gas stream and forms a film on the porous medium.
This stable aerosol or dispersion, may be defined as a stable suspension of a discontinuous liquid phase within another continuous gas phase that is not separable by conventional gas/liquid separation technologies—such as filter-coalescers, residence time coalescers with mesh-pads or vane-packs, etc. For such stability, the discontinuous liquid phase consists of droplets in the 0.1-1-micron range, with the larger droplet end of the spectrum possibly extending up to 10-micron range. This stable aerosol dispersion is necessary to facilitate the first stage of the intimate mass-transfer between the primary and secondary phases. Following the dispersion, the second stage of the invention relates to then using a coalescer such as a porous medium to capture, coalesce, and separate the rich liquid in the form of droplets from the gas. The film of rich liquid on the high surface area porous medium provides a secondary stage for extraction. In order for the porous medium to capture the droplets it must be constituted with fibers that are of such dimensions and interfacial properties as to be able to be “wetted-out” by the liquid, thus enabling it to capture these droplets. This typically requires the fibers to be of the order of magnitude of the droplets; in other words, the porous medium must consist of fibers that are at least in the 0.5-2-micron range. This invention then provides for the contact and separation of the extracting medium in a single device.